Hi!  It's me again.....  I've tried everything this morning and it seems to work perfectly.  so a big thank you to eberyone that answered.

However, I still have a last question regarding this matter.  You said :
"+proj=laea +lat_0=45 +lon_0=-100 +x_0=0 +y_0=0 +a=6370997 +b=6370997 +units=m

 with some modification of +lat_0 and +lon_0 to suit your region."

So, my question : Should I chose approximatly the center of my database for lat_0 and long_0 ?

Thanks!  I hope I posted this msg the correct way this time :)

Roger Bivand <Roger.Bivand@nhh.no> wrote: On Fri, 25 Aug 2006, Philippe Roy wrote:

"Ok, so, in my kriging code, I need to specify a maximum distance in km
(or meter can't remember).  Is this Lambert Azimuthal Equal Area good for
Euclidian distance?  I mean, I need to specify the maximum distance to
consider a station or not for each grid point of my regular grid.  Would
that be good then?

Sorry if it sounds non-understandable! :/ "

(and using an HTML mailer - please do not, it makes thread management very 
difficult!)

Have you tried? (Hint: the metric is meters/metres). Yes, you can give a
maximum distance, otherwise the 2300 by 2300 martix of distances between
stations is unnecessarily large (and it is unlikely that interactions
across the whole region are strong).
                         


> 
> -----Message d'origine-----
> De : Roger Bivand [mailto:Roger.Bivand@nhh.no] 
> Envoyé : 24 août 2006 15:28
> À : Philippe Roy
> Cc : r-sig-geo@stat.math.ethz.ch
> Objet : Re: [R-sig-Geo] Mass conversions of Lat/Long to UTM (many zone)
> 
> On Thu, 24 Aug 2006, Philippe Roy wrote:
> 
> > Hi everyone!  I'm new to R.  I'll try using it for some Kriging.  My aim
> > in the short-term is to convert my 2300 stations database from lat-long
> > to UTM.  This network of stations goes from Virginia to the south, to
> > Montréal to the north, east coast to Michigan in the west.  So, I have a
> > lot of UTM zones to consider.
> > 
> >  
> > 
> > Reading the archives, I've seen this formula to calculate the zones,
> > based on lat-long coordinates :
> > 
> >  
> > 
> > UTM = floor((lon + 180) / 6) + 1
> > 
> >  
> > 
> > So, if I understand correctly, I need to run this formula on each
> > station to get their zone, abnd then I use something like convUL ?
> > 
> 
> If you want to use all the stations together, then they must be in the 
> same zone (otherwise the western edge of the zone will jump for stations 
> in different zones). I think that for continental North America a central 
> UTM zone will not be a very good idea, and that probably a Lambert 
> Azimuthal Equal Area is a better choice.
> 
> You can then use project() or spTransform() in the rgdal package, for 
> example, with EPSG code 2163:
> 
> US National Atlas Equal Area
> 
> +proj=laea +lat_0=45 +lon_0=-100 +x_0=0 +y_0=0 +a=6370997 +b=6370997 +units=m
> 
> with some modification of +lat_0 and +lon_0 to suit your region.
> 
> > 
> >  [[alternative HTML version deleted]]
> > 
> > 
> 
> 

-- 
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Helleveien 30, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
e-mail: Roger.Bivand@nhh.no

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